1. Field of the invention
The present invention relates to an image processing apparatus for use in a digital copying machine. The invention relates, more particularly, to an image processing apparatus with a magnification function for enlarging or reducing a document.
2. Discussion of Background
There are many conventional image processing apparatus which have a magnification function for enlarging or reducing. For example, Japan Patent Laid-Open Publications Nos. 223275/1990 and 277660/1990 disclose such apparatus.
FIG. 13 shows a conventional image processing apparatus which has a magnification function. Input signal D1 is smoothed or emphasized in edge by a matrix of a filter 1 and the signal D2 after the filter 1 is enlarged or reduced by a magnifier 2. In smoothing, the ragged edges of an image are smoothed. In emphasizing, the edges of an image are highlighted. An example of emphasizing is found in Japanese Patent Laid Open No. 252261/1987. Then the signal D3 after the magnifier 2 is converted by a gamma converter 3 and the signal D4 after the gamma converter 3 is gradated by a gradating block 4. The signal D5 after the gradating block 4 is output to a writer. Also as conventional apparatus, there is a device in which a signal is magnified by the magnifier 2 and after that it is smoothed or emphasized in edge by the filter 1.
However, in the conventional apparatus in which the signal is filtered by a filter and after that magnified by a magnifier, the following problem occurs. When the signal is enlarged, the matrix size of the filter can be used effectively, however, when it is reduced, the matrix size of the filter cannot be used effectively. Also in the conventional apparatus in which the signal is magnified by the magnifier and after that filtered by the filter, the following problem occurs. When the signal is reduced, the matrix size of the filter can be used effectively, however, when it is enlarged, it cannot be used effectively.
As a result, in those conventional apparatus, where the order of filtering and magnifying is fixed, there is a problem in the filter cannot be used effectively for at least one of the magnifying and reducing operations.